Assembly And Method To Secure Tubing String to Blowout Preventer

ABSTRACT

A flange assembly and method for securing the downhole tubing string and packer to a blowout preventer is disclosed. The application is particularly useful for high pressure fluid applications downhole such as hydraulic fracking.

TECHNICAL FIELD

This invention relates to oil field operations and in particular, downhole hydraulic fracturing or oftentimes referred to as fracking.

BACKGROUND ART

Fracking is used to increase production from underground hydrocarbonbearing zones. With the recent development of horizontal drilling,wellbores can now penetrate horizontally within a hydrocarbon bearingzone. Fracking, in simplest terms, is a procedure where fluid is pumpedinto the wellbore at a rate sufficient to increase pressure down hole toexceed the pressure gradient of the targeted strata. The rock cracks andthe fracture fluid continues further into the rock, extending the crack.Typically, a proppant is included with the injected fluid such as grainsof sand, ceramic, or other particulates which prevent the fractures fromclosing when injection is terminated. The strata attempts to return toits original condition but the injected particles prevent completeclosure and thus provide pathways for hydrocarbon within the strata tomigrate to the wellbore.

In preparation of a down hole fracking operation, a string of highpressure tubing capable of withstanding high pressures, typically atleast 7,000 psi, is lowered into a well directly above the strata to behydraulically fractured by pumping fluid through the tubing string. Thelower portion of the tubing string is anchored into position using apacker. Depending on the packer used, it is set in neutral, tension orcompression. For example, if the packer is set in compression, thetubing string is rotated causing the seals of the packer to engage theadjacent casing wall and thereafter the tubing string is lowered so thatweight is applied to the packer and the seals firmly engage the casingwall. This requires the tubing string to be lowered possibly severalfeet at the surface and the actual length required is dependent upon howdeep the packer is positioned.

Because of the high pressures associated with fracking, ablow-out-preventer (BOP) is located at the top of the well, typicallybolted to the casing flange which is located at the surface end of thecasing. The BOP seals the annular region between the casing and thetubing to prevent gasses or fluids from escaping the well from thisannular region.

A typical fracking operation will involve multiple diesel truckspowering positive displacement pumps. The discharge from these pumpstypically connect at a manifold and exit the manifold via a single lineconnected to the tubing at the top of the BOP.

Once the packer is set, typical procedure is to apply a backpressure inthe annular region between casing and tubing so it is against thetopside of the packer. This backpressure serves as further insuranceagainst packer failure. However, if the downhole packer fails for anyreason during the fracking operation, the high down hole pressure canact upon the bottom side of the packer and cause the packer and tubingstring to be violently displaced upward out of the well before surfacepumps can be shut down. Any sudden and unexpected movement of the tubingstring upward can cause a serious safety problem not only for thetopside equipment but also for nearby personnel.

SUMMARY OF INVENTION

My invention provides an added level of protection for on-site servicepersonnel during a fracking operation.

The invention is a method and the supportive equipment used for securingthe tubing string to the BOP so in the event of a packer failure, thetubing string cannot violently displace out of the hole before thefracking pumps can be shut down.

The invention provides that the tubing string is secured to the BOP toprevent sudden vertical movement of the tubing string and comprises: a)a threaded flange which is secured to the BOP; and, b) a mandrelthreadably secured to the threaded flange and which operatively connectsto the down hole tubing string and the surface pumps.

The appearance of the threaded flange can be generally described as amodified weld neck flange. The threaded flange comprises a main bodyhaving a plurality of bolt holes passing through the main body andarranged circumferentially and spaced for alignment with correspondingholes on the top flange of a BOP. Preferably, the bottom surface of thethreaded flange has an annular groove for receiving a ring gasket whichwill be disposed between the flange groove and a corresponding groovefound on the top flange of the BOP.

Extending outward from the top surface of the main body of the threadedflange is a neck portion integral with the main body. The neck portionmay be either cylindrical or tapered.

The threaded flange further comprises a central aperture having a firstinside diameter passing through the main body and a second insidediameter passing through the neck portion. The first inside diameter islarger than the second inside diameter. The neck portion furthercomprises a set of female or internal threads for connection to amandrel which is described below. The central aperture is sufficientlywide to accommodate tubing collars to pass through.

A mandrel is provided having a first end and a second end with a set offemale threads at each end. The set of female threads located at thefirst end are for operatively connecting to a down hole tubing stringand the set of female threads located at the second end are foroperatively connecting to surface pumps. The mandrel further comprises aset of male or external threads located at the second end for connectionto the set of female threads located within the threaded flange. Themandrel is sized to be slidably receivable within the central apertureof the main body, by inserting the second end of the mandrel into theaperture of the main body so that the male threads of the mandrel canthreadably engage the female threads of the neck portion. The outsidediameter of the mandrel is therefore larger than the outside diameter oftubing collars used for the tubing string particularly proximal to theBOP.

Preferably, at least one annular groove is provided in the outside wallof the mandrel for positioning of an O-ring which provides a seal to theinner wall of the threaded flange and permits all types of packers to beutilized down hole, including tension, compression or neutral setpackers.

Also preferably, the outside diameter of the mandrel is substantiallyuniform from the first end to the second end and having a pre-determineddiameter. The crest of the male threads is equivalent to the outsidediameter of the mandrel.

Thus, the mandrel is operably connected on one side to the tubing stringbelow and on the other side operably connected to the fracking pumps.The male set of threads on the mandrel is threadably connected to thethreaded flange which is bolted to the BOP after the packer is set.

By securing the tubing string to the BOP, the seals of the BOP are notsubjected to failure as a result of a sudden movement by the tubingstring. This eliminates any chance of gasses or fluids escaping the wellas a result of BOP failure during high pressure fracking operations;thus protecting the health of the nearby personnel as well as thesurrounding environment.

The method of use is as follows and is considered an improvement inflowline assembly for delivering fracking fluid from surface pumps tothe wellbore. In combination with a hydraulic fracturing operation for awell having a hydrocarbon bearing zone and casing string extending up toa surface casing flange, a blowout preventer connected to the casingflange and a tubing string and packer positioned at a pre-determineddepth within the casing string for the delivery of fluid from surfacepumps connected to the tubing string at high pressure, the method forsecuring the tubing string to the blowout preventer comprising the stepsof:

providing the flange and mandrel as described above; operativelyconnecting the first end of the mandrel to the down hole tubing string;positioning the threaded flange upon the mandrel where the lower surfaceof the main body of the threaded flange is facing the blowout preventer;

setting the packer at the pre-determined depth;

rotating the threaded flange to engage the male threads of said mandrel;

aligning the bolt holes on the threaded flange to the bolt holes on theblowout preventer;

securing the threaded flange to the blowout preventer; and,

operatively connecting the second end of the mandrel to the surfacepumps.

A tubing string having a downhole packer is provided for setting thepacker at a pre-determined depth. The top of the tubing string isoperably connected to the mandrel either by direct threaded connectionor indirectly using tubing extensions well known in the art. Above themandrel is typically a short length of tubing for operably connecting tothe discharge from the pump trucks or manifold. However, there can beany number of configurations for the flowline from the pumps to thesecond end of the mandrel. What is to be appreciated is that themandrel, at the second end, is operatively connected to the pumpdischarge line and will be threadably connected to the threaded flangeonce the packer is set. This configuration allows for the tubing stringto travel vertically up or down to set either a tension or compressionpacker and subsequently have the threaded flange rotated to engage themandrel and finally be bolted to the top flange of the BOP. With theflange resting on top of the mandrel before the packer is set,securement to the BOP is quick; requiring only that threaded flange berotated into engagement with the mandrel and then bolted to the BOP.This can be accomplished by a single worker and require approximately 20minutes.

Before the packer is set, the threaded flange does not threadably engagethe mandrel although tubing extends not only below but above thethreaded flange. Since the inside diameter across the neck portion issufficiently large to allow tubing collars to pass, this allows thetubing string to be not only raised but lowered as well.

After the packer is set, the male threaded portion of the mandrel shouldbe located above the top flange of the adjacent BOP at a height topermit threadable engagement with the threaded flange by rotating thethreaded flange about the mandrel and alignment of the bolt holes withcorresponding bolt holes on the BOP. Bolts are then used to secure thethreaded flange to the BOP.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of the flange assembly connectedto a blowout preventer.

FIG. 2 is a side view of the mandrel and connections upstream anddownstream.

FIG. 3 is a side view indicating the positioning of threaded flangeabove the mandrel.

FIG. 4 is a cross-sectional view of the flange assembly and connectionsupstream and downstream.

FIG. 5 is a side view of threaded flange resting upon the mandrel.

FIG. 6 illustrates the rotation of threaded flange to connect to themandrel.

FIG. 7 is a cross-sectional view of the final attachment of the flangeassembly to the blow out preventer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures are provided for illustration purposes and are notnecessarily drawn to scale.

FIG. 1 illustrates an exploded view of my flange assembly 10. Theassembly comprises a threaded flange 12, a mandrel 14, and threadedconnections 16 and 18 for operable connections to the surface pumpsdesignated by P and the tubing string TS respectively. In a preferredembodiment, flange assembly 12 can function up to a maximum pressure ofat least 8,500 psi.

As can best be viewed looking at both FIG. 1 and FIG. 6, threaded flange12 comprises a main body 20 having a plurality of bolt holes H passingthrough the main body and arranged circumferentially and spaced foralignment with corresponding holes H′ located on the top flange of ablowout preventer BOP. Preferably, the bottom surface of the threadedflange has an annular groove G for receiving an API ring gasket R/46 Rwhich will be disposed between annular groove G and a correspondinggroove G′ found on the top flange of the BOP. Threaded flange 12 israted API Series 6-1500 flange which is bolted down with 12 1½ inchbolts 40 and nuts 42 to the top of the BOP.

Extending outward from the top surface of main body 20 is a neck 22integral with the main body.

As shown in FIG. 4, threaded flange 12 further comprises a centralaperture A having a first inside diameter passing through main body 20and a second inside diameter passing through neck portion 22. The firstinside diameter is larger than the second inside diameter. Neck portion22 further comprises a set of female square threads 24 for connection tomandrel 14 which is described below. The central aperture issufficiently wide to accommodate the outside diameter of tubing collarsto pass through.

Mandrel 14 comprises a first end and a second end with a set of 8 roundN-80 female threads at each end and an outside diameter extending fromthe first end to the second end. The set of female threads located atthe first end are for operatively connecting to a down hole tubingstring and the set of female threads 30 located at the second end arefor operatively connecting to surface pumps. Mandrel 14 furthercomprises a set of male square threads 34 located at the second end forconnection to the set of female threads 24 located within threadedflange 12. The crest of male threads 34 is equivalent to the outsidediameter. A pair of annular grooves 36 are present in the outer wall ofmandrel 14 for placement of respective O-rings 38 which permits use ofthe mandrel with all types of packers to be utilized down hole,including tension-compression or neutral set packers. Mandrel 14 issized to be slidably receivable within the central aperture, byinserting the second end of mandrel 14 into the aperture of main body 20so that male threads 34 can threadably engage female threads 24 as shownin FIG. 4.

Having described the individual parts comprising my flange assembly, themethod for assembly will be discussed.

Hydraulic fracturing of a well is a procedure well known. Generally, myinvention is an improvement over the current flowline configuration fordelivering fracking fluid from surface pumps to the wellbore because itprevents upward movement of a tubing string in the event of a packerfailure. For a hydraulic fracturing operation of a hydrocarbon bearingzone and casing string extending up to a surface casing flange, ablowout preventer connected to the casing flange and a tubing string andpacker positioned at a pre-determined depth within the casing string forthe delivery of fluid from surface pumps connected to the tubing stringat high pressure, the method for securing the tubing string to theblowout preventer will now be explained.

Because the desired depth for setting a packer may not position the topcollar of the tubing string at the optimum position for setting myflange assembly 10 to the BOP, an extension 16 can be used for operablyconnecting my flange assembly to the down hole tubing string. Extension16 can comprise one or more tubular parts threaded to one another forconnection to the down hole tubing string TS illustrated in FIG. 2. Asis well known to those having skill in the oilfield services industry,the top collar of the tubing string is held in position using slips (notshown) above the BOP. When the packer is down hole at or near itsintended depth, mandrel 14 is operably attached to the tubing string.Extension 16, mandrel 14 and extension 18 are threadably connected inseries to the top of the tubing string as illustrated generally in FIG.3 along with an O-ring R set upon the top surface of the BOP. In a mostpreferred embodiment, the proximal portion of extension 16 to mandrel 14is spot welded.

Threaded flange 12 is then placed over extension 18 and loweredrepresented by motion L in FIG. 3 until it rests upon the upper edge ofmales threads 34 of mandrel 14 as shown in FIG. 5 and FIG. 6. The packeris set at a pre-determined depth and final movement of the tubing stringis made; the direction of which depends upon the type of packer utilizeddown hole. The final position of the tubing string has the lower surfaceof mandrel 14 on substantially the same plane as the top surface flangeof the surrounding BOP. Next, threaded flange 12 is rotated asrepresented by X in FIG. 6 into threadable engagement with male threads34. Rotation continues until the bottom surface of threaded flange 12contacts the top flange surface of the BOP and bolt holes H align withrespective holes on the BOP. Threaded flange 12 is thereafter secured tothe BOP using bolts 40 and nuts 42 as illustrated in FIG. 7. Afterflange assembly 10 is secured to the BOP, extension 18 is operablyconnected to the surface pumping equipment (not shown).

1. A flange assembly for securing a tubing string to a blowout preventercomprising: a threaded flange comprising: a main body having a lowersurface for engagement with the upper flange of a blowout preventer, aplurality of bolt holes passing through the main body and arrangedcircumferentially and spaced for alignment with corresponding holes on ablowout preventer; a neck portion integral with and extending outwardfrom the main body; a central aperture having a first inside diameterpassing through the main body and a second inside diameter passingthrough said neck portion, said first inside diameter being larger thansaid second inside diameter; said neck portion further having a set offemale threads; and, a mandrel comprising: a first end and a second end,an aperture passing through the mandrel, a set of female threads at saidfirst end for operatively connecting to a down hole tubing string and aset of female threads at said second end for operatively connecting tosurface pumps, and a set of male threads located at said second end;said mandrel slidably receivable within the central aperture of the mainbody of said threaded flange where the female threads of said neckportion can threadably engage the male threads of said mandrel.
 2. Theflange assembly of claim 1 where said mandrel further comprises at leastone annular groove.
 3. The flange assembly of claim 2 where an O-ring ispositioned within each respective at least one annular groove.
 4. Theflange assembly of claim 1 where said mandrel further comprises apre-determined outside diameter from said first end to said second endand where the crest of said male threads is equivalent to saidpre-determined outside diameter.
 5. In combination with a hydraulicfracturing operation for a well having a hydrocarbon bearing zone andcasing string extending up to a surface casing flange, a blowoutpreventer connected to the casing flange and a tubing string and packerpositioned at a pre-determined depth within the casing string for thedelivery of fluid from surface pumps connected to the tubing string athigh pressure, the method for securing the tubing string to the blowoutpreventer comprising the steps of: providing a threaded flangecomprising: a main body having a lower surface for engagement with theupper flange of a blowout preventer, a plurality of holes passingthrough the main body and arranged circumferentially and spaced foralignment with corresponding holes on a blowout preventer; a neckintegral with and extending outward from the main body; a centralaperture having a first inside diameter passing through the main bodyand a second inside diameter passing through said neck, said firstinside diameter being larger than said second inside diameter; said neckfurther having a set of female threads; and, a mandrel comprising: afirst end and a second end, an aperture passing through the mandrel, aset of female threads at said first end for operatively connecting to adownhole tubing string and a set of female threads at said second endfor operatively connecting to surface pumps, and a set of male threadslocated at said second end; said mandrel slidably receivable within thecentral aperture of the main body of said threaded flange where thefemale threads of said neck threadably engage the male threads of saidmandrel; operatively connecting the first end of said mandrel to thedownhole tubing string; positioning the threaded flange upon saidmandrel where the lower surface of said main body is facing the blowoutpreventer; setting the packer at the pre-determined depth ; rotating thethreaded flange to engage the male threads of said mandrel; aligningsaid plurality of holes on the threaded flange to bolt holes on ablowout preventer; securing said threaded flange to said blowoutpreventer; and, operatively connecting the second end of said mandrel tothe surface pumps.